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Caltech Geologists Find New Evidence That Martian Meteorite Could Have Harbored Life

California Institute of Technology
Pasadena, CA

Contact: Robert Tindol
(818) 395-3631
tindol@caltech.edu

March 13, 1997

Caltech Geologists Find New Evidence That Martian Meteorite Could Have
Harbored Life

PASADENA -- Geologists studying Martian meteorite ALH84001 have found new
support for the possibility that the rock could once have harbored life.

Moreover, the conclusions of California Institute of Technology researchers
Joseph L. Kirschvink and Altair T. Maine, and McGill University's Hojatollah
Vali, also suggest that Mars had a substantial magnetic field early in its
history.

Finally, the new results suggest that any life on the rock existing when it
was ejected from Mars could have survived the trip to Earth.

In an article appearing in the March 13 issue of the journal Science, the
researchers report that their findings have effectively resolved a
controversy about the meteorite that has raged since evidence for Martian
life was first presented in 1996. Even before this report, other scientists
suggested that the carbonate globules containing the possible Martian
fossils had formed at temperatures far too hot for life to survive. All
objects found on the meteorite, then, would have to be inorganic.

However, based on magnetic evidence, Kirschvink and his colleagues say that
the rock has certainly not been hotter than 350 degrees Celsius in the past
four billion years -- and probably has not been above the boiling point of
water. At these low temperatures, bacterial organisms could conceivably
survive.

"Our research doesn't directly address the presence of life," says
Kirschvink. "But if our results had gone the other way, the high-temperature
scenario would have been supported."

Kirschvink's team began their research on the meteorite by sawing a tiny
sample in two and then determining the direction of the magnetic field held
by each. This work required the use of an ultrasensitive superconducting
magnetometer system, housed in a unique, nonmagnetic clean lab facility. The
team's results showed that the sample in which the carbonate material was
found had two magnetic directions -- one on each side of the fractures.

The distinct magnetic directions are critical to the findings, because any
weakly magnetized rock will reorient its magnetism to be aligned with the
local field direction after it has been heated to high temperatures and
cooled. If two such rock fragments are attached so that their magnetic
directions are separate, but are then heated to a certain critical
temperature, they will have a uniform direction.

The igneous rock (called pyroxenite) that makes up the bulk of the meteorite
contains small inclusions of magnetic iron sulfide minerals that will
entirely realign their field directions at about 350 degrees C, and will
partially align the field directions at much lower temperatures. Thus, the
researchers have concluded that the rock has never been heated substantially
since it last cooled some four billion years ago.

"We should have been able to detect even a brief heating event over 100
degrees Celsius," Kirschvink says. "And we didn't."

These results also imply that Mars must have had a magnetic field similar in
strength to that of the present Earth when the rock last cooled. This is
very important for the evolution of life, as the magnetic field will protect
the early atmosphere of a planet from being sputtered away into space by the
solar wind. Mars has since lost its strong magnetic field, and its
atmosphere is nearly gone.

The fracture surfaces on the meteorite formed after it cooled, during an
impact event on Mars that crushed the interior portion. The carbonate
globules that contain putative evidence for life formed later on these
fracture surfaces, and thus were never exposed to high temperatures, even
during their ejection from the Martian surface nearly 15 million years ago,
presumably from another large asteroid or comet impact.

A further conclusion one can reach from Kirschvink's work is that the inside
of the meteorite never reached high temperatures when it entered Earth's
atmosphere. This means, in effect, that any remaining life on the Martian
meteorite could have survived the trip from Mars to Earth (which can take as
little as a year, according to some dynamic studies), and could have ridden
the meteorite down through the atmosphere by residing in the interior cracks
of the rock and been deposited safely on Earth.

"An implication of our study is that you could get life from Mars to Earth
periodically," Kirschvink says. "In fact, every major impact could do it."

Kirschvink's suggested history of the rock is as follows:

The rock crystallized from an igneous melt some 4.5 billion years ago and
spent about half a billion years on the primordial planet, being subjected
to a series of impact-related metamorphic events, which included formation
of the iron sulfide minerals.

After final cooling in the ancient Martian magnetic field about four billion
years ago, the rock would have had a single magnetic field direction.
Following this, another impact crushed parts of the meteorite without
heating it, and caused some of the grains in the interior to rotate relative
to each other. This led to a separation of their magnetic directions and
produced a set of fracture cracks. Aqueous fluids later percolated through
these cracks, perhaps providing a substrate for the growth of Martian
bacteria.

The rock then sat more or less undisturbed until a huge asteroid or comet
smacked into Mars 15 million years ago. The rock wandered in space until
about 13,000 years ago, when it fell on the Antarctic ice sheet.